Cytokines are small molecular weight proteins that have a myriad of biological functions. For example, cytokines are known to be capable of stimulating their own synthesis, as well as the production of other cytokines from a variety of cell types. They are also associated with disease. A good example is the presence of the cytokines interleukin-1 (IL-1) and tumor necrosis factor (TNF) that alone or in combination cause a shock state in animals that hemodynamically and hematologically is characteristic of septic shock in man caused by bacterial infection. Also,TNF, in addition to playing a critical role in sepsis, has recently been shown to be involved in initiating the expression of human immunodeficiency virus in human cells that carry latent virus. Folks et al., 1989, Proc. Natl. Acad. Sci. USA, 86:2365. Thus, preventing or inhibiting the formation of the 17 kD, or lower molecular weight forms of TNF would be a valuable prophylactic for the treatment of AIDS patients by preventing the expression of virus that is latent in the patient. TNF and IL-1 also play a role in various autoimmune diseases, particularly arthritis. Duff, et al., 1987, International Conference on Tumor Necrosis Factor and Related Cytotoxins, 175:10.
It is thus becoming apparent that aside from their normal biological functions, which have not been fully elucidated, that cytokines are associated with systemic changes arising from infection and tissue injury.
In addition to IL-1 and TNF, another cytokine, IL-6, also termed hybridoma growth factor, interferon-beta-2, B-cell stimulatory factor 2, 26 kilodalton protein, and hepatocyte stimulating factor, is involved in infection, particularly sepsis, as well as in affecting the growth of tumor cells. Indeed, Hack, et al., 1989, Blood, 74:1704, have shown that a significant number of patients with sepsis display increased plasma levels of IL-6, and that the amount of IL-6 correlates with the symptoms of shock and with clinical prognosis. In the sepsis patients shown in that report, serum IL-6 levels were on the order of 1,000 U/ml.
Although the precise pathology of bacteremia is not completely elucidated, it is believed that bacterial endotoxins, lipopolysaccharides (LPS), are the primary causative agents. LPS consist of at least three significant antigenic regions, the lipid A, core polysaccharide, and O-specific polysaccharide. The latter is also referred to as O-specific chain or simply O-antigen. The O-specific chain region is a long-chain polysaccharide built up from repeating polysaccharide units. The number of polysaccharide units differs among different bacterial species and may vary from one to as many as six or seven monosaccharide units. While the O-specific chain varies among different gram-negative bacteria, the lipid A and core polysaccharides are similar if not identical.
IL-6 acts on a variety of cells including lymphocytes, hepatocytes (causing the production of acute phase protein synthesis) hematopoietic stem cells and nerve cells. It may act as either a growth factor, a growth inhibitor, or even a differentiation inducing factor. Kishimoto, T. and Hirano, T., 1988, Annual Review of Immunology, 6:485-512. It has recently been suggested that IL-6 is an autocrine growth factor for renal cell carcinomas. Miki, S., et al., 1989, FEBS, 250:607-610. Thus, compounds that interfere with the autocrine activity of IL-6 may be effective chemotherapeutics.
Native IL-6 has a molecular weight of 19-30 kD and an immunoreactive species of 60-70 kD has also been reported (see Kelfgott, et al., 1989, J. Immunol., 142:948 and Jablon, et al., 1989, J. Immunol., 142:1542). The gene coding for a human IL-6 polypeptide has been cloned and expressed as shown by the following European patent applications: EPA 0 220 574, published May 6, 1987, to Revel, M, et al., entitled "Human interferon beta2A and interferon-beta2B, vectors containing genes coding for said interferons, cell lines producing same and use of said interferons as pharmaceuticals"; EPA 0 254 399, published Jan.27, 1988, to Clevenger, W., et al., entitled "B-cell stimulating factor"; EPA 0 257 406, published Mar. 2, 1988, to Kishimoto, T., et al., entitled "Recombinant B-cell differentiation factor"; EPA 0 261 625, published Mar. 30, 1988, to Honjo, T., et al., entitled "Human B-cell differentiation factor and process of producing said factor"; EPA 0 267 779, published May 18, 1988, entitled "Human pleiotropic immune factor and muteins thereof"; and PCT WO 88/00206, published Jan. 14, 1988, to Clark, S., et al., entitled "Production and use of IL-6".
As mentioned above, IL-6 has been cloned from a number of animal species, including human and mouse. Human IL-6 consist of 184 amino acids with 4 cysteine residues. Hirano, T. et al., 1986, Nature, 324:73. Human IL-6 cDNA shares a good deal of homology with murine IL-6 cDNA. Indeed, at the DNA level human IL-6 shows a 65% homology with murine IL-6, and at the protein level there is 42% homology. The position of the 4 cysteine residues is conserved. Curiously, the sequence of IL-6 is significantly homologous to G-CSF. In addition, the position of the 4 cysteine residues of IL-6 match those of G-CSF. This suggests a common functional similarity between the two molecules, as well as their possible origin from a common ancestor gene.
No doubt cytokines will be found to play a role in diseases other than those mentioned above. Nevertheless, the importance of cytokines in disease, particularly sepsis, is readily apparent when the extent of the disease is considered. In the United States alone nosocomial bacteremia develops in about 194,000 patients, and of these about 75,000 die. Maki, D.G., 1981, Nosocomial Infect., (Dikson, R.E., Ed.), page 183, Yrke Medical Books, U.S.A. Most of these deaths are attributable to six major gram-negative bacilli, and these are Pseudomonas aeruginosa, Escherichia coli, Proteus, Klebsiella, Enterobacter and Serratia. The current treatment for bacteremia is the administration of antibiotics which, unfortunately, have limited effectiveness. Thus, it will be appreciated that there is an ongoing clinical need for medicaments that can be used by the physician to regulate the affects of cytokine production.